JPH08114421A - Non-contact type measuring device for measuring thickness ofmaterial body comprising transparent material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noncontact type measuring device for measuring the thickness of an object formed of a transparent material out of contact therewith. SOLUTION: There are provided first and second radiation sources 10, 20 for generating a beam, first and second beam deflecting devices 14, 24 formed of a transparent material, and first and second detecting devices 16, 26 disposed adjacent corresponding thereto. Two beams radiated from the first and second radiation sources 10, 20 are passed through the deflecting device having reflecting and refracting boundary surface through first and second separating surfaces 141, 241, and then obliquely applied to a material 1 to be measured. The first and second component beams are reflected on the front surface 101 and the rear surface 102 of the material 1 to be measured to direct to the second and first detecting devices 26, 16 through the second and first beam separating surfaces 241, 141. In order to reduce the size of the device and facilitate precise measurement, the first and second separating surfaces 141, 241 are taken as incident surfaces of the deflecting device facing the radiation sources 10, 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type measuring device for measuring the thickness of an object made of transparent material. More particularly, in this device, two opposing beams emitted from the first and second sources are directed through the first and second beam separators and through the deflecting device. The deflecting device is made of a transparent material and has reflecting and refracting interfaces, and two opposing beams are transmitted through the deflecting device and are to be measured (hereinafter referred to as an object to be measured). Is directed diagonally (at a given angle) to the plane of
The first and second component beam pairs are then reflected by the front and back surfaces of the object to be measured and again transmitted through the deflecting device and the first and second beam separators and directed to the first and second detection devices. Such a non-contact type measuring device.

[0002]

2. Description of the Related Art A method of obliquely directing a laser beam on the surface of a glass plate to measure its thickness is known, for example, from EP-A-0,248,552. The laser beam is partially reflected by the glass plate and partially refracted into the glass plate. The refracted component is
It is then partially reflected on the back side of the glass plate. The components reflected on the back surface then impinge on the front surface again and are refracted and emitted from the glass. If the front and back surfaces are parallel to each other, this component beam is displaced parallel to the component beam reflected directly on the front face. The spacing between the two component beams is directly proportional to the angle of incidence with respect to the glass surface and the glass thickness if the glass refractive index is constant.

The required oblique incidence of the laser beam on the surface of the object to be measured is, according to the state of the art, generally by obliquely setting the laser or by using one or more mirrors or by deflection. This is done by using a prism. A device of the above type is described in DE-A 4,143,186. The device described in this patent publication is designed to correct a measurement error that occurs when the object to be measured is tilted, for example.
It has two opposing beam paths. This known device has two laser sources, two beam separators, two linear sensors and a deflection prism. The opposing beam paths are such that the optical components are symmetrically arranged on the deflection prism such that the symmetry axis of the deflection prism defines the symmetry axis of the entire device.

[0004]

The disadvantage of the above device is that all the measurement beams do not count the surface of the object to be measured, but along their path from the light source to the detection device, the eight glass / air interfaces (beams). It must be transmitted through a separator, a deflection prism). This adversely affects the measurement accuracy because the interface is easily contaminated, especially when using such equipment in manufacturing plants. Furthermore, the two beam paths cannot be manipulated at the same time, or must be manipulated alternately because parasitic (or derivative) reflections interfere with the measurement. These parasitic reflections are caused by each incident beam and, after reflection at the beam separator, will overlap the component beam pair to be detected. It is therefore an object of the invention to determine the distance between the front and rear reflective interfaces, in particular of the thickness of objects made of transparent material, of the type mentioned above, which enables even small glass thicknesses to be measured quickly and with high accuracy. It is to provide a non-contact type measuring device.

[0005]

The non-contact type measuring apparatus of the present invention measures the distance between the reflection boundary surfaces of the front surface and the rear surface, in particular, the thickness of an object to be measured, which is made of a transparent material, and reflects the front surface and the rear surface. It defines the boundary surface. This non-contact measuring device,
First and second radiation sources (radiation sources or light sources) for generating first and second beams, first and second beam deflecting devices made of a transparent material, and among the beam deflecting devices, First and second arranged in close proximity to the corresponding one of
Position-resolved detection device, wherein the first deflection device has a first surface directed toward the first radiation source, and the second deflection device is directed toward the second radiation source. The first surface is separated from the beam incident surface by the first surface, and the first surface is separated by the first surface. Together defining a separating surface which enters the deflecting device and forms a first component beam directed to the object to be measured along the first beam path, the second surface being the beam incident surface and the separating surface. A second beam is separated at the second surface to enter a second deflector at the second surface and a second component beam directed toward the object under measurement along a second beam path. It defines both the separation surface to be formed and the first
And a second deflecting device, the first beam path and the second beam path in which the first component beam and the second component beam travel toward each other and obliquely strike the front boundary surface.
Are arranged in a relationship that defines the beam path of
Here, (a) the radiation of the first component beam is reflected toward the second deflecting device at both boundary surfaces of the front surface and the rear surface, and along the direction of the second component beam. The radiation of the first component beam is separated from the second component beam by passing through the second deflecting device to reach the second surface, and at the second position. And (b) the radiation of the second component beam is reflected towards the first deflector at both the front and rear interface and the first deflector is reflected toward the resolving detector. Through the first deflector along the direction of the component beam to reach the first surface, where the radiation of the second component beam is from the first component beam. It is separated and reflected towards the first position-resolved detection device.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The deflector is made of a body of transparent material and has refracting and reflecting interfaces used to deflect the beam. The invention is based on the knowledge or idea that the deflecting device can be shaped so that its interface can be used as a first and a second beam separator.
The device according to the invention, in contrast to the prior art, does not require a beam separator. There are many possibilities for realizing a deflection device of the type described above. A person having knowledge of geometrical optics will find it easy to find a mode or embodiment of the deflecting device which is suitable for the intended purpose, since the beam path is customarily given.

A preferred embodiment is, for example, a deflecting prism of the type described in DE-A 4,143,186, in which the beam reflected back from the object to be measured is shown in said publication. As such, it is dimensioned such that it does not exit the prism through the sidewalls, but is reflected by the sidewalls toward the upper substrate on which the detector is mounted. The laser must be properly oriented towards the sides of the deflecting prism. These sides of the deflecting prism act as beam separators in this aspect of the invention as described below.

The invention is preferably realized by constructing the deflecting device from two identical prisms which are arranged symmetrically with respect to the symmetry axis of the device in order to obtain opposite beam paths. Each prism is shaped and dimensioned such that the beam entrance surface directed to the corresponding source is simultaneously a reflection surface for the component beams of the other laser beam reflected by the DUT. In other words, the component beam is directed to this detector at this interface (reflection surface).
Is reflected by. Therefore, this boundary surface is not only a part of the beam deflecting device but also functions as a beam separating surface at the same time.

In a preferred mode, the first and second surfaces of the first and second prisms are coated with a beam separation film, and the first and second prisms are respectively attached to the object to be measured. It has a facing third surface and a fourth surface, and the third surface and the fourth surface are coated with a non-reflective film. In addition, the first prism emits radiation of the second component beam to the first
Having a fifth surface that is transparent to the position resolution detection device of
On the other hand, the second prism has a sixth surface through which the radiation of the first component beam is transmitted toward the second position-resolved detection device, and the third and fifth surfaces jointly form the first surface. of defining the angles beta _1, the surface of the fourth and sixth are defining a second angle beta ₂ jointly similarly, the angle beta ₁ wherein the first radiation of a second component beam Is selected to pass vertically through the fifth plane towards the first position-resolved detection device, while the second angle β ₂ is such that the radiation of the first component beam is in the second position-resolved position. It is chosen to pass vertically through the sixth surface towards the detector. More preferably, the first angle β ₁ is selected such that parasitic radiation in the first prism is totally reflected in the first prism, while the second angle β _{2 is} Is selected such that the parasitic radiation in the second prism is totally reflected in the second prism. A first absorption filter or an interference filter interposed between the fifth surface and the first position resolving and detecting device;
A second absorption filter or an interference filter interposed between the sixth surface and the second position resolution detection device may be further included.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings illustrating the embodiments. In FIG. 1, reference numeral 1 represents an object to be measured, for example, a glass plate or a glass tube whose thickness or thickness is to be measured. Reference numerals 10 and 20 denote the first and second radiation sources, respectively, and in this example, the laser light source. Reference numerals 12 and 22 denote beam converters which serve to form the beam cross section into a desired shape and to change the polarization direction of the beam as necessary. Sign 1
Reference numerals 4 and 24 respectively denote prisms, and each prism functions as a deflecting device and a beam separator. Sign 1
6 and 26 show the associated detectors for the reflected component beam, which in the illustrated embodiment are linear sensors. The measurement signals from the linear sensors 16 and 26 are sent to the electronic evaluation device 30 for evaluation. The overall shape is 2
It is plane-symmetric with respect to an axis of symmetry extending in the plane of the drawing between the two prisms 14 and 24. The reason for such plane symmetry is that opposing beam guidance is required to correct the measurement error caused by the inclination of the DUT 1. In this regard, reference is made to DE-A 4,143,186. The measurement principle is described in detail in this publication.

During operation, the beams emitted from sources 10 and 20 pass through beam converters 12 and 22, respectively, and then to the outer surface 141 (first side) of prisms 14 and 24.
Surface) and 241 (second surface). Although a part of the component of the radiation is reflected by these boundary surfaces 141 and 241, most of the component is refracted and enters the individual prisms. The incident beam is reflected by the boundary surface 142 (third part) of the prism.
Surface) or 242 (fourth surface), a part thereof is reflected again and a part thereof is refracted. The refracted component of the beam exits the prism and strikes the DUT. Advantageously, the prism is shaped as described below so that the reflected component beam remains within the prism and does not appear as a parasitic reflection.

For clarity, the beam path in the prism to the object to be measured is shown schematically in FIG. It should be noted that, in this figure, the opposite component beams of the other beam paths reflected by the DUT 1 are not drawn. Figure 2
Similarly to FIG. 3, only the prism 14 on the left side of FIG. 1 is shown. Since the shape is symmetrical, the beam path is the same for both prisms.

FIG. 3 shows the beam path of the component beam back-reflected in the prism. The back-reflected component beams are reflected by the front surface 101 and the rear surface 102 of the DUT 1, reach the surface 142 of the prism 14, and a part of each component beam is reflected again by the surface 142, and the reflection of each component beam is performed. The portion that did not enter the prism 14 is refracted as shown. The refracted component beam traverses the prism and is reflected by the surface 141 toward the surface 143 (fifth surface). This component beam pair is
After leaving the prism 14 at 43, the linear sensor 16 is reached.
The measurement signal is evaluated by the electronic evaluation device 30 connected to the linear sensor 16 and converted into an interval value.

The evaluation of the measurement signal is according to the prior art, for example European Patent Publication 0,248,
No. 552. The evaluation is essentially performed by using the following formula (1).

[Equation 1] Depending on the electronics to be implemented, it may be necessary to introduce a correction factor into the above formula. For example, position detection photodiodes or diode detectors arranged in a line are suitable as the detection devices 16 and 26, and are collectively referred to as linear sensors in this specification. The linear sensor is preferably used because it is durable, has high resolution, is small in size, is geometrically stable, is relatively inexpensive, and is easy to evaluate.

As shown in FIGS. 1-3, the outer surfaces 141, 241 of the prisms 14, 24 not only deflect the beam, but also separate the beam. Sources 10 and 2
The incident beam from 0 strikes each outer surface 141, 241 of prisms 14 and 24 and is refracted into the prism. On the other hand, the back-reflected component beams are transmitted to the outer surfaces 141 and 24.
1 is reflected in the direction of the linear sensors 16 and 26. This indicates that the surfaces 141 and 241 have beam separation characteristics. Therefore, it is sufficient that the surfaces 141 and 241 can partially transmit the radiation. This is usually the case for any radiation with respect to any interface between the air and the object of transparent material. Since the beam paths face each other, it is necessary to separate the beams. That is, the radiation reflected back by the DUT is partially separated from the radiation emitted by another radiation source and advances into the DUT, so that the radiation is separated from the other radiation and detected. It must be biased by the device. To do so, the device disclosed in DE-A-4,143,186 comprises a separate optical component, namely a beam separator. According to the invention, the need for these separate optical components, and the absence thereof, leads to the above advantages.

The dimensions of prisms 14 and 24 are dependent on the particular application, and those skilled in the art will readily be able to determine the optimal dimensions for that application. To determine this dimension, one of ordinary skill in the art must know about the underlying geometrical optics and that the beam path shown in FIG. 1 is essentially realized. . The dimensioning of the prism is usually performed by the following method. Those skilled in the art will choose the dimensions of the prism such that the beam incidence angle γ directed at the surface of the object to be measured will be between approximately 20 and 70 °. In this way, between the maximum beam spacing that can separate the back-reflected component beams and the limit of lateral expansion of the measured area of the device under test, which is mainly associated with thick symmetrical objects. A compromise is established. Further, the geometry of the prisms 14 and 24 is such that the angle given to a given dimension is such that the total internal reflection at the sides 143 (fifth surface), 243 (sixth surface) causes parasitic reflections to remain within the prism. It can be selected by determining β. For example, parasitic radiation may occur when the radiation traveling toward the object to be measured is reflected by the bottom surface of the prism facing the object to be measured. If the parasitic reflections do not stay within the prism, they will reach the linear sensor and further generate a signal that complicates the evaluation and degrades the signal / noise ratio (S / N ratio). Apart from achieving a highly accurate measurement, by eliminating the effects of these parasitic reflections, both beam paths are used simultaneously, unlike the device disclosed in DE-A-4,143,186. The advantage is that you can. The effects of the parasitic reflections of the beam path appearing in the known device do not occur in the device of the invention.

Advantageously, the component beam pair reflected by the device under test is directed vertically onto the surfaces 143, 243 after being reflected by the respective boundary surfaces 141, 241 of the respective prisms 14 and 24. This can be conveniently done simply by adjusting the prism angle β. When perpendicularly transmitted through the surfaces 143 and 243, the prism is
Acts as an anamorphic expansion or expansion system.
That is, the interval S ₁ between the two component beams reflected by the front surface 101 and the rear surface 102 of the DUT ₁ is expanded to S ₂ by the prism. Since the component beams leave the prism and reach the linear sensors 16, 26 directly, the spacing remains wide even when the measurement signal is processed. The enlargement ratio V is given by the following equation 2 from FIG.

[Equation 2] When the object to be measured is thin, there is an advantage that the reflection intensity distribution can be separated again. These intensity distributions from the anterior and posterior surfaces will overlap each other without widening. In this way even thin glass can be measured which would have been impossible to measure without magnification.

In the preferred embodiment of the present invention, the linear sensors 16, 26 are the interfaces 143, between the prisms 14, 24.
It is directly fixed to 243. Preferably, an absorption filter or an interference filter, especially one consisting of a dielectric layer system, is arranged between said interface and the linear sensor in order to filter out radiation coming from the surroundings. To do this,
For example, the filter may be joined between the boundary surface and the linear sensor. It has been found to be particularly successful with the colored glass filter RG 645 which suppresses short wavelength radiation below 645 nm. In this way, all glass surfaces are optically inactive, free from contamination, and no special requirements regarding smoothness or polish quality are required. Between the reflected beam and the transmitted beam, the beam separating coatings having a ratio of the reflected radiation to the transmitted radiation of about 1: 1 are provided on the surfaces 141 and 24.
By coating No. 1, the component beam can be detected with high intensity. Coating the surfaces 143, 243 with a non-reflective coating will often prevent the formation of the parasitic reflections.

With respect to the above, the preferred materials and dimensions for the constituent prisms were measured. These dimensions and the angle γ determined thereby are listed in Table 1 below.

[Table 1] The angle γ in Table 1 above is defined by the beam leaving the prisms 14 and 24 toward the DUT 1 and the corresponding surface 142,
It represents the angle between the 242 normal or the angle between the normal to the surface of the object to be measured and the beam directed to this surface.
Large angles of γ are particularly suitable for measuring small glass thicknesses, so that they can be measured in small workspaces. On the other hand, a small angle of γ is particularly advantageous when measuring larger glass thicknesses or when a large workspace is desired. The angle γ (and thus the prism angle α) determines the accuracy. In comparison, the angle β is less critical. This is because, if the paths perpendicular to the surfaces 143 and 243 are deviated by ± 1 °, the sine of the angle that determines the refraction changes by only 0.01%. According to the law of refraction, Only a slight beam deflection occurs.

[0020]

The advantages of the device according to the invention are summarized as follows. (A) By including several functions in one component, that is, by providing one prism with the functions of beam separation and beam deflection, the device according to the present invention can be made compact and inexpensive. (B) No separate beam separator is required. (C) Furthermore, the device according to the invention requires little or no dielectric coating. (D) A solution found in DE-A 4,143,186 which overcomes the eight interfaces between glass and air (not including the DUT) in order to reduce reflections and which must be treated. Unlike the method, the shape shown in FIG. 1 need only consider four glass / air interfaces.
In addition, the prism angle can be chosen so that parasitic reflections (which cannot be completely eliminated even after the surface has been treated to reduce reflections) do not affect measurements in other beam paths. it can. Therefore, it is possible to evaluate both beam paths at the same time, which increases the measurement speed.

The feature of the device according to the invention is that it is easy to adjust because the two laser optical axes are simply set parallel to each other and at the same time aligned with the front edge of the device which also serves as the reference edge of the prism. Especially. The reference edge is represented schematically by the line 150 in FIG. If the angle α of the prism is made very precise, it can be assumed that the angle of incidence on the DUT is automatically the same for both beam paths, as long as the prism is placed at the reference edge at faces 142,242. The device according to the present invention is suitable for various applications other than the measurement of the thickness of the sheet glass, and the measurement of the wall thickness of the glass tube is interesting. For thin tubes, the device according to the invention is provided with the appropriate dimensions, and the wall thickness and the inner and outer diameters of the tube can be measured. Corresponds to the reflection of the beam on the front and back walls of the tube during the measurement, with a constant distance from each other 2
Two reflective pairs are obtained. The outer diameter corresponds to the distance between the 1st and 4th reflections (with respect to the zero point of the measuring scale).
The inner diameter corresponds to the distance between the second and third reflections. Furthermore, spacing and planar measurements can also be performed on opaque objects that reflect primarily in one direction. For these objects, the distance of the first reflection to the reference point on the measurement scale is important.

Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and those skilled in the art can describe the spirit of the present invention and the scope of claims. It will be apparent that various changes and modifications can be made without departing from the scope of.

[Brief description of drawings]

FIG. 1 is a schematic view of the overall shape of a measuring device according to the present invention.

FIG. 2 is a schematic diagram of the beam path of a beam entering a prism from a source.

FIG. 3 is a schematic view similar to FIG. 2, showing the beam path of the reflected component beam in the prism.

[Explanation of symbols]

1 to-be-measured object, 10 1st radiation source, 20 2nd radiation source, 12 1st beam converter, 22 2nd beam converter, 14 1st prism, 24 2nd prism, 16 1st line Shape sensor, 26
Second linear sensor, 30 Electronic evaluation device, 101
Front surface of the measured object, 102 rear surface of the measured object, 14
1 1st surface, 241 2nd surface, 142 3rd surface, 242 4th surface, 143 5th surface, 243
6th surface, 150 Reference edge, b Length of 3rd and 4th surfaces, h Height of prism measured from 3rd and 4th surfaces

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Georg, Sparschus Germany, 55459 Aspishheim, Fritz-Hüxel-Strasse 2

Claims (9)

[Claims] 1. A non-contact type measuring apparatus for measuring a distance between front and rear reflection boundary surfaces, particularly a thickness of an object to be measured, which is made of a transparent material, and defining a front and rear reflection boundary surfaces. And a first and a second radiation source for generating a second beam, a first and a second beam deflecting device made of a transparent material, and a light source disposed close to a corresponding one of the beam deflecting devices. A first and a second position resolving detection device provided, wherein the first deflection device is directed toward the first radiation source.
And the second deflecting device has a second surface directed toward the second radiation source, the first surface being a beam entrance surface and the first beam being Separating surface at the first surface to enter the first deflecting device at the first surface and form a first component beam directed to the object under measurement along a first beam path. And the second surface separates the second beam from the beam incident surface and enters the second deflecting device at the second surface. And a separating surface which forms a second component beam directed to the DUT along a second beam path, the first and second deflecting devices mutually defining the first and second deflecting devices. A first beam path and a second beam path in which the component beam and the second component beam travel toward each other and obliquely strike the front boundary surface. Are arranged so as to define the beam path of the first component beam, and (a) the radiation rays of the first component beam are directed toward the second deflecting device at both boundary surfaces of the front surface and the rear surface. Radiation of the first component beam is reflected and transmitted through the second deflector along the direction of the second component beam to the second surface, where the radiation of the first component beam is The second component beam is separated from the second component beam and reflected toward the second position-resolved detection device, and (b) the radiation of the second component beam is at the interface between the front surface and the rear surface. The light is reflected toward the first deflecting device and is transmitted through the first deflecting device along the direction of the first component beam to reach the first surface, and at the first surface, the first The radiation of the second component beam is separated from the first component beam Non-contact type measuring apparatus characterized by being reflected toward the first position-resolving detector device. 2. The non-contact measuring device according to claim 1, wherein the deflecting device comprises first and second prisms symmetrically arranged with respect to each other. 3. A beam separation film is coated on the first surface and the second surface of the first and second prisms, and
The first and second prisms respectively have a third surface and a fourth surface facing the object to be measured, and the third surface and the fourth surface are coated with a non-reflective film. The non-contact measuring device according to claim 2. 4. The first component beam and the second component beam are directed toward the object to be measured, respectively.
Through the surface of the first prism, the first prism is sized such that the first component beam is emitted at an exit angle γ between 20 ° and 70 °, while the second prism is Non-contact measuring device according to claim 3, characterized in that the second component beam is also radiated with an exit angle γ between 20 ° and 70 °. 5. The first prism has a fifth surface through which the radiation of the second component beam is transmitted toward the first position-resolved detection device, while the second prism is The sixth component surface has a sixth surface through which the radiation of the first component beam is transmitted toward the second position-resolving detection device, and the third and fifth surfaces jointly form a first angle β ₁ . And the fourth and sixth surfaces likewise jointly define a _second angle β ₂ , wherein the first angle β ₁ is the radiation of the second component beam Of the first component beam to the second position-resolved detection, while the second angle β ₂ is selected so as to pass vertically through the fifth surface towards the position-resolved detection device. 5. The non-contact measuring device according to claim 3, wherein the non-contact measuring device is selected so as to vertically pass through the sixth surface toward the device. 6. The first angle β ₁ is selected so that the parasitic radiation in the first prism is totally reflected in the first prism, while the second angle β ₁ is selected. 6. The non-contact measuring device according to claim 5, wherein ₂ is selected so that parasitic radiation in the second prism is totally reflected in the second prism. 7. The first position resolution detection device is the fifth position resolution detection device.
The linear detection device fixed to the surface of the
The non-contact measurement device according to claim 5 or 6, wherein the position resolution detection device is a linear detection device fixed to the sixth surface. 8. A first absorption filter or an interference filter interposed between the fifth surface and the first position resolving detection device, and the sixth surface and the second position resolving detection device. The non-contact type measuring device according to any one of claims 5 to 7, further comprising a second absorption filter or an interference filter interposed therebetween. 9. The non-contact measuring device according to claim 5, wherein the first and second prisms have the following dimensions for specific types of glass.